Category: Powershell

Adam Bertram shows how to use regular expressions for pattern matching in Powershell:

However, regex has traditionally been a topic that most IT pros shy away from when they first see how it works. Admittedly, regex does take a bit of getting used to, and you’re still probably going to have to do some Googling every time you need to use it. But learning how PowerShell integrates regex into its language is a skill that’s much easier learned and one that will come in handy often.

First of all, when someone says “working with regex,” that can mean a lot of things so let’s break it down a little bit. Regex is a method of string matching. Its sole purpose is to match and parse strings from within other strings. This can mean a lot of things and PowerShell allows you to do just about anything here, particularly as it has the full power of the .NET Framework. For our purposes, let’s investigate a few ways PowerShell allows you to match strings and how to parse strings with regex and PowerShell.

Read on for a couple sample scenarios.

Klaas Vandenberghe notes a discrepancy in how Measure-Object works, based on syntax:

So, is the -InputObject parameter broken? Not really, but we need to be aware of the logic behind it.
Maybe we are used to work with -ComputerName for a lot of cmdlets and functions, and we rely blindly upon the ability of the command to handle whatever collection we provide. We know this executes the action we chose, like Get-DbaSqlService or Get-DbaOperatingSystemor whatever, separately to every computer in the collection. The collection is ‘fold out’, ‘unpacked’, ‘split’.

-InputObject doesn’t do that! Is that wrong? Not necessarily, it may be a choice of design to have possibilities to enquire the properties of the collection itself and those of the ‘members’ or ‘children’. It’s just a surprise the behaviour differs from pipeline input to parameter input.

Something to keep in mind when writing Powershell scripts.

Jeff Hicks shows off some of the niceties of Powershell’s ConvertTo-HTML cmdlet:

This is because Convertto-Html, like Export-CSV and Export-Clixml, take the entire object. This is not just the default result you see on the screen. Remember, everything will be treated as a string. In my example, if I want a similar HTML file, I will have to recreate the output with Select-Object. This might require piping the original result to Get-Member to discover the “real” property names.

It won’t output beautiful results, but with the appropriate CSS theming, you can generate good internal reports.

Chrissy LeMaire shows how to save the dbatools module to install it offline:

There are essentially 3 ways to get the zip of our module

1. From PowerShell Gallery using Save-Module

2. From PowerShell Gallery by downloading from powershellgallery.com/api/v2/package/dbatools

3. By downloading from dbatools.io/zip

Read on to see examples for each of the three methods.

Adam Bertram shows how to write safer code by validating parameters:

Simply adding [Parameter()] to the parameter block makes this function “advanced.” Once we have this in place, we can then add in some parameter validation code. In our case, we need to ensure that the file provided with FilePath actually exists before proceeding. To do this, we’ll use the ValidateScript attribute which allows us to run any code we want. As long as it returns $true, it will allow the function to run.

function Set-File {
param(
[Parameter()]
[ValidateScript({ Test-Path -Path $_ -PathType Leaf})]
[string]$FilePath
)
}

Notice that I used the pipeline variable $_ in this example. This represents whatever value the parameter is. If the user provides a file path that does not exist, they will be notified.

Read the whole thing.